linux-kernel - Re: [RFC 1/2] virtio_net: timeout control virtqueue commands

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Message-ID: <CAJaqyWe--Hho9EdweqkC-h9=t5vhY0cbAN9uAw=hATpkSMbsEg@mail.gmail.com>
Date: Thu, 16 Oct 2025 08:25:31 +0200
From: Eugenio Perez Martin <eperezma@...hat.com>
To: "Michael S. Tsirkin" <mst@...hat.com>
Cc: Jason Wang <jasowang@...hat.com>, Maxime Coquelin <mcoqueli@...hat.com>, 
	Yongji Xie <xieyongji@...edance.com>, virtualization@...ts.linux.dev, 
	linux-kernel@...r.kernel.org, Xuan Zhuo <xuanzhuo@...ux.alibaba.com>, 
	Dragos Tatulea DE <dtatulea@...dia.com>
Subject: Re: [RFC 1/2] virtio_net: timeout control virtqueue commands

On Thu, Oct 16, 2025 at 8:22 AM Michael S. Tsirkin <mst@...hat.com> wrote:
>
> On Thu, Oct 16, 2025 at 02:03:57PM +0800, Jason Wang wrote:
> > On Thu, Oct 16, 2025 at 1:45 PM Michael S. Tsirkin <mst@...hat.com> wrote:
> > >
> > > On Thu, Oct 16, 2025 at 01:39:58PM +0800, Jason Wang wrote:
> > > > > >
> > > > > > Not exactly bufferize, record.  E.g. we do not need to send
> > > > > > 100 messages to enable/disable promisc mode - together they
> > > > > > have no effect.
> > > >
> > > > Note that there's a case that multiple commands need to be sent, e.g
> > > > set rx mode. And assuming not all the commands are the best effort,
> > > > kernel VDUSE still needs to wait for the usersapce at least for a
> > > > while.
> > >
> > > Not wait, record. Generate 1st command, after userspace consumed it -
> > > generate and send second command and so on.
> >
> > Right, that's what I asked in another thread, we still need a timeout
> > here.
>
> we do not need a timeout.
>
> > Then I think it would not be too much difference whether it is
> > VDUSE or CVQ that will fail or break the device. Conceptually, VDUSE
> > can only advertise NEEDS_RESET since it's a device implementation.
> > VDUSE can not simply break the device as it requires synchronization
> > which is not easy.
> >
> > > But for each bit of data, at most one command has to be sent,
> > > we do not care if guest tweaked rx mode 3 times, we only care about
> > > the latest state.
> >
> > Yes, but I want to know what's best when VDUSE meets userspace timeout.
> >
> > Thanks
>
>
> userspace should manage its own timeouts.
>

Can we just apply the patch 2/2 of this RFC directly and apply the
VDUSE CVQ on top then? What are we missing to do it?

On Thu, Oct 16, 2025 at 8:22 AM Michael S. Tsirkin <mst@...hat.com> wrote:
>
> On Thu, Oct 16, 2025 at 02:03:57PM +0800, Jason Wang wrote:
> > On Thu, Oct 16, 2025 at 1:45 PM Michael S. Tsirkin <mst@...hat.com> wrote:
> > >
> > > On Thu, Oct 16, 2025 at 01:39:58PM +0800, Jason Wang wrote:
> > > > > >
> > > > > > Not exactly bufferize, record.  E.g. we do not need to send
> > > > > > 100 messages to enable/disable promisc mode - together they
> > > > > > have no effect.
> > > >
> > > > Note that there's a case that multiple commands need to be sent, e.g
> > > > set rx mode. And assuming not all the commands are the best effort,
> > > > kernel VDUSE still needs to wait for the usersapce at least for a
> > > > while.
> > >
> > > Not wait, record. Generate 1st command, after userspace consumed it -
> > > generate and send second command and so on.
> >
> > Right, that's what I asked in another thread, we still need a timeout
> > here.
>
> we do not need a timeout.
>
> > Then I think it would not be too much difference whether it is
> > VDUSE or CVQ that will fail or break the device. Conceptually, VDUSE
> > can only advertise NEEDS_RESET since it's a device implementation.
> > VDUSE can not simply break the device as it requires synchronization
> > which is not easy.
> >
> > > But for each bit of data, at most one command has to be sent,
> > > we do not care if guest tweaked rx mode 3 times, we only care about
> > > the latest state.
> >
> > Yes, but I want to know what's best when VDUSE meets userspace timeout.
> >
> > Thanks
>
>
> userspace should manage its own timeouts.
>
> > >
> > > --
> > > MST
> > >
>